The current inventors reported, in the 24th International Conference on Low Temperature Physics—LT24 Conference Proceedings 850, 471 (2006), the growth of high quality, large size, crack free films of YBCO (YBa2Cu3O7-x) on top of r-cut Sapphire with a buffer layer of YSZ (Yttrium-stabilized ZrO2).
According to this report, both YSZ and YBCO layers were grown by off axis dc magnetron sputtering from stoichiometric single targets. The YSZ layer was sputtered at 5 mTorr of Ar with the substrate at 955° C. The thickness of the YSZ was 100 nm, deposited at a deposition rate of 0.01 nm/sec. During the sputtering of YBCO the heater temperature was 930° C. The substrate was heated by IR radiation and its temperature was estimated as 750° C. The gas mixture was 50/50 percent oxygen and argon at 200 mTorr. The dc power on the target was 140 W, yielding a sputtering rate of about 0.03 nm/sec. An annealing process in pure oxygen was performed for 16 hours at approximately 500° C.
The thickest layer reported was about 1000 nm thick, and had critical current density of about 0.2 MA/cm2 (See FIG. 3 of the report), which at the given thickness is equivalent to critical current of 20 A per cm width.
Other publications that may serve for understanding the background of the invention include:    1. N. Klein et al., J. Appl. Phys. 67, 6940 (1990).    2. G. Kästner et al., Phys. Stat. Sol. (a) 150, 381 (1995).    3. A. G. Zaitsev et al., Applied Superconductivity: Inst. Phys. Conf Ser. 158, 25 (1997).    4. A. G. Zaitsev et al. J. Supercond. 11, 361 (1998).    5. R. Wördenweber, Supercond. Sci. Technol. 12, 86 (1999).    6. C. Zuccaro et al., IEEE Trans. Appl. Supercond. 1, 295 (1997).    7. R. Wordenweber et al., IEEE Transactions on Applied Superconductivity 9, 2486 (1999).    8. K. Develos-Baraginao et al., Supercond. Sci. and Tech. 20, L25 (2007).    9. K. Develos-Baraginao et al., Supercond. Sci. and Tech. 18, 667 (2005).    10. Yu N. Drozdov et al., Supercond. Sci. Tech. 9, A166 (1996).    11. M. S. Rao et al., J. Appl. Phys. 79, 940 (1996).    12. R. Krupke et al., Physica C 317-318, 536 (1999).    13. B. Almog et al., Supercond. Sci. Technol. 18 (2005) 1441-1444    14. “Epitaxial Growth of Supercondcutors of SSIFFS” by Goal et al., presented at High Temperature Superconductivity program Peer Review of the USA Department of Energy on Jul. 30, 2008, available on the Internet at http://www.energetics.com/supercom/08/pdfs/presentations/wednesday/research/1% 20SR %20Strategic%20Substrate%20Development%20for%20Coated%20Conductors.pdf